Microstructure and optical properties of Co-WC-Al2O3 duplex ceramic metal-dielectric solar selective absorbing coating prepared by high velocity oxy-fuel spraying and sol-gel method

Metal-dielectric composite coating has wide application for solar selective absorbing coating in concentrating solar power (CSP) systems. A novel Co-WC-Al2O3 duplex ceramic metal-dielectric composite solar selective absorbing coating were prepared by combined high velocity oxy-fuel spraying (HVOF) with sol-gel method. Al2O3 particles were added to the Co-WC absorbing layer to improve the solar selectivity and thermal stability of the composite coating. The phase structure, the surface and cross-section morphologies and optical properties of the single absorbing coating prepared by the HVOF process were systematically investigated by XRD, SEM, EDS and spectrophotometers. Moreover, the optical properties and thermal stability of the composite coating with Al2O3 anti-reflection layer, as well as the internal structure of the annealed coating were also measured and analyzed in detail. Results showed that the composite coating exhibited excellent solar selectivity, the absorptance/emittance was 0.908/0.145. After annealed at 600°Cfor 7 days in air, the absorptance/emittance slightly decreased to 0.898/0.172, which indicated that the coating exhibited a good thermal stability.